OBJECTIVE To understand the neural system underlying the expression of emotion in primates. RESULTS We have focused on elucidating mechanisms underlying the expression of fear and anxiety. This is an area of great importance because, when appropriate, fear-motivated behaviors are adaptive; however, when overly intense or expressed out of context, extreme fear is characteristic of many forms of psychopathology. We are using state-of-the-art techniques to understand the role of the amygdala and its nuclei in mediating fearful states. We will assess the role of the amygdala in mediating 1) classically conditioned autonomic responses, 2) ethologically relevant threatening stimuli, and 3) affiliative and defensive behavior expressed in social situations. This year fifteen monkeys have been lesioned using ibotenic acid. These axon sparing lesions are resulting in more subtle alterations then those reported with more destructive lesioning. Specifically, the data suggests that amygdala lesions disrupt the ability to express learned fears. Eventually, these studies will define biolog ical mechanisms regulating the expression of the primateUs adaptive responding to threatening stimuli. These findings will provide insight into mechanisms mediating maladaptive responding in humans, which is characteristic of fear-related psychopathology. FUTURE DIRECTIONS Histological analysis of all lesions are being performed to correlate site and extent of lesions with effects KEY WORDS neurobiology, amygdala, defense, behavior, brain, psychopathology, conditioning FUNDING NIMH MH46729 PUBLICATIONS Kalin NH, Shelton SE, Rickman M, Davidson RJ Individual differences in freezing and cortisol in infant and mother rhesus monkeys. Behav Neurosci. 122(1):251-254, 1998. [J] Kalin NH, Larson C, Shelton SE, Davidson RJ Asymmetric frontal brain activity, cortisol, and behavior associated with fearful temperaments in rhesus monkeys. Behav Neurosci. 112(2):286-292, 1998.[J] Kalin NH, Shelton SE Ontogeny and stability of separation and threat-induced defensive behaviors in rhesus monkeys during the first year of life. Am J Primatology 44:125-135, 1998. [J] SE Shelton, RJ Davidson, NH Kalin Extreme right frontal EEG activity is associated with elevated CRH levels. Presented at the Society for Neuroscience, Los Angeles, CA, November 1998. [A]